Mass ballast for MT prop — required?

[haykinson]

Hi folks,

During my annual, the shop pointed out that I have an MT 3-bladed prop on my plane, but no mass ballast in the nose. They are suggesting that this is a required thing, and are pointing at an email they got from Diamond suggesting as much.

My airplane had a 3-bladed MT prop since 2008, and as far as I can tell nobody has removed the ballast. Is it really required? I'm not looking forward to the additional 17 lbs removed from my useful load, all of a sudden. If it is / is not required, does anyone know how to validate that?

[Chris]

As far as I know it is not required. It just might be more difficult to stay within the CG envelope without it, so it's a common mod on the Lycoming G1000 models. I think it moves the CG forward about 0.5 or 0.6 inches.

[Soareyes]

I see you have a 2007 XLS model. 40 gallon tanks or 50? TAS active traffic?

Going from memory here, in 2007 they added some equipment pretty far back in the fuselage, specifically the TAS Active Traffic. This made the plane tail heavy. Most of those were XL models. Additionally, 50 gallon tanks restricted the aft end of the allowable CG range compared to the previously common 40 gallon tanks. The ballast in the nose was added to bring the CG forward into the new shorter CG envelope.

With the XLS model they repositioned the TAS Traffic unit a bit more forward. That helped the CG but with 50 gallon tanks you may still need some weight in the nose, either a metal prop or the nose ballast.

Theoretically your logbook should show if the ballast was removed but I wouldn't count on it.

It's not a bad idea to re-weigh a plane. Get your new weights, plug them into the W&B calculator of your choice, see where it comes on the CG graph. Outside the aft end of the envelope? Add the ballast. I think I have a set in the hangar if you need it.

[CFIDave]

This short answer is that ballast in the nose for the MT prop is NOT required.

We used to own an early DA40XLS (2008 model built in late 2007) that came with no ballast in the nose, despite having the lighter 3-bladed MT prop. It wasn't until later -- part-way through 2008 -- that Diamond started delivering DA40 XLS aircraft with the nose ballast standard to make the back seat more useful. We also had the Avidyne TAS600 active traffic unit (standard on 2007 XL, but optional on 2008+ XLS DA40s) installed under the rear seat instead of in the rear fuselage to help with CG.

The balance of our DA40 without nose ballast (and 50 gal tanks) was such that with 2 adults in the front seats, we had to place luggage in the back seat instead of the rear baggage compartment to avoid exceeding the rear CG limit. But without the ballast, we had about 20 lbs more useful load.

[haykinson]

I see you have a 2007 XLS model. 40 gallon tanks or 50? TAS active traffic?

50gal, with TAS. yeah.

It's not a bad idea to re-weigh a plane. Get your new weights, plug them into the W&B calculator of your choice, see where it comes on the CG graph. Outside the aft end of the envelope? Add the ballast. I think I have a set in the hangar if you need it.

I'd never done this. How does re-weighing a plane work? And for "plug them into the W&B calculator", I assume you mean with typical loads for my missions etc?

This short answer is that ballast in the nose for the MT prop is NOT required.

I'd run into trouble showing that this is the case. A Diamond tech's email says that it is, but I figure there's got to be some regulatory backing to this.

The balance of our DA40 without nose ballast (and 50 gal tanks) was such that with 2 adults in the front seats, we had to place luggage in the back seat instead of the rear baggage compartment to avoid exceeding the rear CG limit. But without the ballast, we had about 20 lbs more useful load.

I've never found this to be the case for me. Maybe I'm not very heavy or whatnot, but two adults in the front keep me within the envelope, with full fuel.

[CFIDave]

The balance of our DA40 without nose ballast (and 50 gal tanks) was such that with 2 adults in the front seats, we had to place luggage in the back seat instead of the rear baggage compartment to avoid exceeding the rear CG limit. But without the ballast, we had about 20 lbs more useful load.

I've never found this to be the case for me. Maybe I'm not very heavy or whatnot, but two adults in the front keep me within the envelope, with full fuel.

We had no W&B problem with 2 adults in the front seats and full fuel -- the issue was that IF we also carried luggage, it needed to go in the back seat area rather than in the rear baggage compartment.

[Rich]

Weighing the plane is described in the Maintenance Manual. If done, be sure it's done correctly. Mine has been weight 4 times.
1. Diamond factory at initial delivery
2. Diamond factory upon their installation of the extended baggage.
3. A shop nearby in Bend after installation of the MTOW/MLW SB.
4. A shop at my home field with me carefully observing, as #3 was clearly not correctly done.

1 and 2 showed discrepancies in the station measurements, causing a not credible difference in CG.

[CFIDave]

This short answer is that ballast in the nose for the MT prop is NOT required.

I'd run into trouble showing that this is the case. A Diamond tech's email says that it is, but I figure there's got to be some regulatory backing to this.

So what's the regulatory document that requires nose ballast? There was a running change to Diamond's production that included the installation of nose ballast in new aircraft, but I'm unaware of any AD that *requires* it to be added to planes like my DA40 XLS with 50 gal tanks and MT prop that were delivered without it.

[Soareyes]

With an XLS model your TAS Traffic box is probably under the back seat instead of in the rear fuselage. But still, with 50 gallon tanks and a composite prop you may well benefit from installing the nose ballast. If the ballast was removed in the distant past the W&B calculations you are using now may be way off. You may be running a more rearward CG than you think.

Luckily the DA40 is forgiving. And the restriction of the back end of the CG envelope is only there because with 50 gallon tanks installed the plane didn't quite pass spin testing at the most rearward CG. They just moved the limit forward until it did pass. It's not like the plane becomes uncontrollable when loaded to the same limit as the 40 gallon planes.

Not to say you shouldn't respect CG limits, especially to the rear. A plane loaded too far aft can indeed become uncontrollable.

Weighing the plane is supposed to be done by a mechanic. They will record in the aircraft logbook a new basic empty weight and moment arm to plug into your W&B calculator. Without these accurate numbers you don't know what your CG is doing.

So why do I have a spare set of ballast plates in the hangar? My 2008 XLS also came with the nose ballast because I ordered the lighter Hartzell composite prop and the factory just stuck it on as a matter of course. But I also got 40 gallon tanks allowing for a longer CG limit. I don't think it had the TAS either. At the time of delivery I asked the dealer to remove the ballast, showing them the W&B calculations that it wasn't needed. They had to check with the factory but eventually agreed. The ballast has been in a box since.

Weighing the plane will settle the question with numbers, not opinions.

[greg]

This short answer is that ballast in the nose for the MT prop is NOT required.

I'd run into trouble showing that this is the case. A Diamond tech's email says that it is, but I figure there's got to be some regulatory backing to this.

I can't see how there can be a regulatory requirement - my 2007 XL came from the factory without the ballast, and was used by a US flight school for six years like that. If there was any requirement to add the ballast, there would need to have been some MSB or AD issued to cover the "faulty" aircraft that were already in the field. (I had the ballast added when I bought the plane because I wanted the flexibility to carry people in the back seats.)